Retarded air circulating dental oven



2 Sheets-Sheet l INVENTOR Z7 f www ATTORNEY CIA E. SHOUDY RETADED AIR CIRCULATING DENTAL OVEN Filed Feb. nl5, 1928 Dec. 1, 1931. c. P. SHOUDY RETARDED AIR CIRCULATING DENTAL OVEN 1928 2 Sheets-Sheet 2 Filed Feb.

INVENTOR lae'er/kouqy Mad y ATTORNEY Patented Dec. 1, 1931r` uNm-:Df smrrs. -P1ATENT1OFFICE? CHESTER P; SHOUDY, OF SPOKANE, 'WASHINGTON RETARDED A11-3., CIRGULATVING nnrrrlu. OVEN The object of this invention is to provide a novel means for preparing a dental investment for thecasting operation. y

One of the features ofthis invent-ionis to not vonly subject the, 'investment to a dry high temperature heat, but also to a heat that is inthe form of circulating heated air,

v and it is a further feature to not only retard the circulation 'of the air but to interpose v'd10 the investment in and substantially expose the latter to the circulating air in such a inannerthat the investment will be substan-y tially uniformly desiccated.`v

A further feature resides in subjecting t-he 15 investment tothe action of a current of heated air that is retarded' both as regards its rate of ingress and egress. Y l y A further feature consistsy inrproviding a heater shell or body vwith a bore for passage of the air therethrough and disposing yelectrical heating means along the interior of the bore for heatingandjcausing circulation of the air, the air being soretarded as to play upon `the interposed investment in a manner to equally affect all portions of the' latter by reason of such retardation, not-With-` `standing the fact that the investmentV is ,disposed out of contact with the heating means andv radially inwardly rthereof.,v l

One of the special features of the invention is to provide a Aheater in `'which different degrees of temperature can be maintained without Vany fluctuation below the minimumtemperature,so. that in any-event, the investment is prevented Vfrom cracking due to any'expansion. Afurther feature is to provide an improved means Whereby after the investment is -once disposed. in the heater, its preparation for casting can be not vonly completed, but quickly completed, Without changingr the position ofthe investment from the position in which it Was initially disposed inthe heater.V

A further feature consists in means Whereby one character or'degree of temperature 'may be employed to effect the performance of one-stage of treatment of the investment,

and another character or degree of tempera- 'ture for another stage of treatment tl1rOf 4cuit a high heat adjustment.

Y, appunti lea'rebruary 15,1928. serialA No.v254,523.

A further feature resides in providing a casing for the heater and operatively or structurally connecting theV casing with the heater in a manner to provideV for a constant vand free circulation of air betweenv the tWO to thereby prevent the exterior of the heater from burning its support. `i y 3 A further feature resides in novel means vWhichnot only functions asl `an'air control,

but also as a means of imparting a pre-00 "liminary heatingtreatinent to a plurality of investments While that investment in the heateris undergoingtreatment. y

My invention hasmany other features and objects which Will be more fully described 65A in connection lwith the accompanying drawings' `and which `vvill be more Aparticularly In the drawings :---V j i j Fig 1 isa vertical sectional view of the 7l most preferred "form of myV invention.

Fig. 2 isa sectional view on line 2 2 of Fig.y 1. l j c Fig. y3 is a( sectional vievv'on'line 3-3 of Figl'. V 'I Fig; 4 is a diagrammatic view pointed out in'andby the appended claims.

of the cir- Fig. `5 is a partial view thereof in a low heat adjustment. Y -Like' characters of vvreference designate 80 similar parts throughoutthe different figures jef the drawings; f

In the specific formshown, I have illustrated What I Will generallyterm an insulating casing and While it is not essential. to the^ invention'rthat this casing made yof any particular material, by reason of the novel v association of the casing withthe heater, Still, I prefer to make thewcasing of earthen Ware, n

and have so'` shown the saine.` Said casing 90 includes'a cylindrical portion l, having 'an open top 2, The lower portion is belled as shown at 3, partly to lend supporting stability Y to the structure. I also provide the supporting or lower portion 3 with one `or vmore air 95 1 ingressy openings 4, the purpose of which will be later defined.V The casing is provided with heater supporting ,means whichmay be in the fformof" an internally projecting l vflange 5.' j

kas indicated by the arrows.

. be described.

A heater supporting means is provided which is shown in the form of a disc-like grill the same having a generally imperforate central portion (i, and a series or" openings which may be formed by a plurality of lugs 7, projecting radially outwardly and adapted not only to be supported on flange 5, but also to center the grill eoncentrically in the casing and afford passages for upward travel of air Near the central portion of the supporting'grill, I pro-- vide what I will term an air ingress opening 8, which will later be more `fully described in function. On the upper face of the supporting grill I provide means which may be an annular recess 9, for supporting andcentering my improved heater body, to be presently described. Inside ot said annular recess 9,

I provide the upper tace of the supporting grill with a flange 10, adapted to center an investment support which I have shown in the torni of a Greek cross, the wings ot which I have indicated at 11. I desirably make this support for the investment ot relatively thin material, such as metal, and dispose the same on edge so thatits restriction of movement of the air will be reduced to a minimum. Further, this winged or Greek cross form ot support functions as a guide to theupwardly flowing air to keep the latter in channels, for a portion oi' the travel of the air, as will later This form of investment support permits me to dispose the same directly over the air ingress opening S, without any appreciable interference with air flow, which is an advantage that will later be functionally developed. Y

It will now be clear that with the construction shown, I am able to make the grill support of earthen material and avoid precision fitting of parts, and that the elements so far described are easily assembled, and readily renewable, and are noty encumbered with movable fittings or attachments.v

Reference will next be made lto my iini proved heater body and the manner` in which the latter coacts with the scribed. i

rSaid heater body is shown in the torni lelements, ust ydeof a cylindrical shell 12 of a suiliciently reduced diameter or size with respect to the v.casing as to permit of an ample insulating :flow of airfin the annular and vertical passage resultantly formed, as indicated at 13.- Said i body 12, `is preferably formed of earthen material and is open at both ends and forms,

by reason of its bore, a heating air passage v'which I` will designate at A. The lower end 1dmaybe seated and centered on the supporting. grill by engagement. with the walls of l.recess 9, and-itwill now be clear that except iter the ingressopening 8, the lower end of Mthe body 12 is closed by the supporting grill. ,The heater body 12is provided on its interior with means for heating the air in passage A and causing circulation upwardly of such air in the upright passage A, and as shown, said means is electrical. I have provided' the body 12 with a series of radially inwardly projecting and vertically extending ribs 15 and 1G, in alternate order, there being six ot eac-h, in the pieseiit construction. Coils of resistance wire are mounted on ribs 16 and a` length of coil is disposed in each chamber or channel termed by the adjacent ribs 15 and 16,' as shown in Fig. 3. I will generally designate the coils at 17 and-will later referto an electrical diagram for tracing thecurrent therethrough. However, in the description of the present phase of the structure, it will be clear that the coils are strung on ribs 1G and that the ends 18 and 19, of said ribs, are suitably recessed, as shown in Fig. 1, to accommodate said coils. The investment to be desiccated, is generally indicated at B, and it will be clear that the latter is disposed concentrically inwardly lwith respect to and out of engagement with the heating means described and it will also .be clear that the disposition of the investment Y than ingress opening 8, to take care oit expansion ot the heated air and the central disposition oi said openings insures a radial inward iifiovement et' the heated air, as will be later described.

`I will next describe a feature whereby the device of my invention serves to treat a plurality of investments, in a preliminary maiiier, to facilitatel the final treatment when anyone thereof disposed in the heater.

The closure 20, is shown providedwith a plurality of elevated ribs 23, which as shown iii Fig. 2, extend across the upper face thereot. Said ribs are suitably interrupted by the opening 22 and preferably terminate short ot the peripheral edge ot the closure. One or more investments, as indicated at C, may be disposed on said closure and the ribs 23 torni aircliannels in which the heated air travels outwardly and about the investments C. A heat retaining and air restricting cap 24:,pre1i`- ei'ably ot earthen material, is disposed over the investments C, as shown, and rests on the closure 20, annularly about the outer ends oi' ribs 2?), so to be effectively centered on the closure 120. Said cap 24, is provided with a handle 25, through which a vent 2G, extends.

`This 'vent` 26', is ,relatively-l restricted to ref tardthe passage ofV heated air therethrough, 'when 4the additional investments are bemg `treated.'-`IIowever, thedevice` oifmy inventienis clear-ly operative when they Lcap 24,

is -removed or' omitted.;

g Referencewill neXt be madeto the' diagrammatic circuit' \'vhich is shown in Figs. 4

andf, illustrating the means whereby I can apply different 'temperatures for different stages of treatment of the investment.

wrklltli'e `coils 17, are 1n one* continuous'cir cuit and in Fig.'4, I haveshown all the coils of one half of the heaterat and the remaining coilsat E, which simplifies the illustrationpof the circuit. I have shown a switch having terminals 27 and 28, connected with lines 29 and 30, respectively. Y vOne end coil conductor 31, is connected with line 29, at

32, andthe remaining coil end conductor 33, fis-connected" with terminal 34.' Aniintermediatecoil conductor 35, is connected with ter- '1`ninal`36lk Terminal 28 isconnected by strap }37- With terminal^38 and terminal y39 is connected `by 40, with'terminal 34. The switch.

"the device isf connected with a usual voltage lamp socket, then one `hundred and 'tenvolts would be entering the coils through conduc- Ators 31`and 3 3, and leaving' through inter mediate `conductor 35,as indicated by the ar- V'-rows. Specifically, the current would pass from line29, through'27, 46, 45, 47, 39, 40 and 34, to conductor lFrom conductor 35,thecurrent would leave' through'36, A43, 41,44, 38, 37,'28/,and 30.` T his hook-up would afford high heat temperature inthe ,passage v,-oit the heater body 12.

To obtainv a. low heat, theswitchwould be adjusted to the Fig. `5, or`series'iposition;V In this position, contacts`46 and 47A are inopen vcircuit relation to terminals 27 'andi 39, re-

v spectively, andthe currentwould lflow from j 29 to k31, through'the coils and backthrough 33 to34,4 3, 41, 44, 28.V and out through line 30. Ineither position of the switch, all the 'coils'will be rin circuit and consequently,an

even and vsteadyheat will be transmitted. I have shown av switch 4S, mounted in' one of the openings`4, of the casing and accessible `from the exterior thereof `for the heatadj ustment just described and I deem it unnecessary to show` electrical connections from switch" vr48,' tothe coils17, in viewfof the illustration in Figs. 4 and 5.

Iwill next-'describe the operation ,otmy

improved heater andthe manner and method in which it lfunctions.

.Y Asfoneofthe main objects ofi the invention )is to prepare an investment vfor the casting operation, Il will iirstbriefly ydescribethe investment shown. As usual, the linvestment material 49;, is disposedina metal cylinder or band V50'and the lowerend 51, is fiat, whereas and its usual functionis to receive the gold, in casting.V I have shown a wax pattern of an inlay, at 53, andthe bore 54,is,:t`o rm`ed by withdrawal of the sprue Wire. The investmentqmaterial, at this stage of the work,

7o thefupp'er end visconcave, as indicated at 52. vThis cavity; 52, is made by thesprue former' Which is considered as being before the heater has lbeen started/is very Iwet, andconsequently, not porous.` Therefore, I'first desire to drive the water out ofthe investment material preferably to` such an extent as todes-y switch 48, to correspond tothe `low( heat or `series adjustment, as shown inF 5,-send- I ing the current through all'the coils 17.k This generates a `constant :heat that issufficiently high to drive off the water and 'yet not sutleiently'high to melt the wax pattern. This .low heat never fluctuates downwardly, hence,

there can be no danger of cracking the in- `vestment. If anything, this low heat,by reason of the heatv accumulation in the refractory heating body, rather increases slightly, asthefirst stage of desiccationisbeing carried on. Now after the water has' been driven off from the investment,|the latter becomes porous, and capable of initiating and sustainf ing capillary attraction. i :The Ynext stage of the'operation consists in getting rid of the wax pattern to leavel the mold cavityfree for gold casting. Hence, after driving ofi' the water, I change the switch tothe high heat adjustment shownr Fig. 4, wherein allthe'lcoils "17 are likewise in service, but twice' the'amount' of# current ,is entering ea'ch'conduetorl and`33,that iwas only ,entering one-of sadj`cond'uctors,"in the low heat Iadjustment. v'seen that I'e'an-use the same lamp socket attachment for both degrees ofk heat, which is Thus, it will be a very great; convenience. f Of course, inthis last stage, of treatment,

j or Wax melting stage, ythe investment' will' be inverted from the position shown in Fig.11 .to'dispiosev th'exc'a'vity end 52, lowermost. In Vsome instances, oriaccordig tothe requirements or methods of the operator, the investyment may vbe initially disposed in such inlVerted 'position yand retained in throughout the treatment.

As the temperature. increases, the Wax pattern will melt and when it becomes sufficiently such position liquid, capillary Hattraction -will draw the melted wax in all directions through thepolrous investment and the'exposed ends thereof will finally `aiiiord. an, outlet for the melted waxandthe latter willA finally be entirely destroyed, leaving the investment completely j free therefrom. Further, thishigh heat will i'ccateA they same, vand .to do this, I adjust `also destroyall residues in the mold cavity 'investments on closure 20, as indicated at C,

andfthey willl be subjected to a preliminary drying out action that will greatly hasten the first stage of treatment when such investments Lhavelater been disposed in the heater. The heated air will not only engage the bottoms of the investments C, but the peripheries, inpassing toward thev outlet 26. By reason of-the fact that the `outlet 26 is relatively restricted with respect to the volume of heated air that enters cap 24, it will retard passage of said air and hence the tops of said investment will also-be acted upon by said air.

I nextdesire to point out a very important feature of my `invention whereby substantially uniform heat is applied to the investment B that is interposed in the path of the heated air.

Because of the restriction afforded by opening v22, to an absolutely free and unrestrained egress of the hot air, there will be a certain resistance against free and unrestrained ingress through opening 8. Therefore, as such ingress is relatively slow, the air will not be able to vrush toward the bottom 5l, of the investment but will quickly be heated as it ascends,and before it reaches the bottom 51,

itfwill be atmaximum temperature. According to my theory, the airv heated near the vlower ends of the coils will rise, vbut will also travel radially inwardly as it rises and will therefore merge with the incoming cold air entering ingress opening 8, and be heated to a maximum temperature almost as soon-as it enterspassage A. Further, the wings 11, of the investment support (which substantially fully expose the bottom and periphery of the investment) forln channels acting to facilitate mixture of the hot air ascending from the lower `rends 4of the coils 17 and the cold air entering through opening S. It will also be noted that after the heater has been started, the air that has passed through openings 4, will have been thoroughly warmed before it enters passage A.

It will now be clear thateven the lower- .most end of the investment, which is engaged affectedy by the fact that egress opening122 the chamber A. l It will also be noted that after the heater has been started, and before the investment has been inserted, the air entering openingsll, will have been thoroughly warmed before it enters through ingress 8, in fact, such vair will have been warmed above room temperature.

New it should be clear that even though the investment Bis out of contact-with the heating means 17, and disposed radially inwardly thereof, still, because of the circulating restraint imposed upon the hot air, the latter will play uniformly upon not only the ends but the entire periphery of the investment. At first, the exposed ends of the investment will have the water driven therefrom and thus become porous, and then these exposed ends, partly because of their' porosity, and partly because of the capillary attraction thus resulting, will greatly aid in drawing water from inner portions of the investment toward the ends thereofA to effect the consummation of desiccation.

It is believed that my invention will be fully understood from the foregoing description and while I have herein shown and described one specific form of my invention, I do not wish to be limited thereto except for such limitations as the claims may import.

I claim:

1. In a retarded air circulating dental oven, a refractory body having an upright air passage therethrough, electrical heating means on the wall of said passage for heating and causing circulation of air through said passage, means for supporting an investment substantially centrally of said passage and between the ends thereof, and closures for the ends of said passage having relatively compensatively reduced` openings disposed axially of saidpassage for retarding movement of the heated air and causing the latter to play upon all portions of the investment.

2. In an electric heater' of the class described, an outer casing having an open top andfprovided with an air ingress opening near its lower portion,`a hollow heater body disposed in spaced relation in said easing for free How of air therebetweema grill removably supported in said casing and having a generally imperforate portion supporting #i said heater body and having an air ingress opening communicating with said body and supplied by Warm air entering said casing, and a winged investment support resting on said grill over said ingress opening and said wings forming channels for mergence of incoming air and heated air flowing toward and exposing the lower portions of said investment thereto.

Y 3. i In an electric heater for preparing dental investments for casting, Aa heater bodf v i having an upper open hot air discharge en and a lower air ingress end, a closure for said upper end having an egress opening for discharge of the heated air, said closure having elevated portions on its upper face for supporting one or more investments for prelimi- Y nary heating thereof, and a cap engaging said elosure'and adapted to enclose said investments and provided with an egress opening for the heated air. e f

In Witness whereof I have hereunto set my hand and seal. 1

CHESTER P. s'HoUDY. 

